The Sheffield utility knife Neal had in his pocket is the kind of thing sold at hardware and sporting-goods stores all over the city. At the time, that model and ones more or less identical to it were stocked at Auto Zone, Pep Boys, Home Depot, Paragon Sports, and several other reputable hardware and outdoor-gear shops in the five boroughs. It's the kind of thing your outdoorsy uncle might carry. Today you can buy one on Amazon for less than 15 bucks.
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Nonetheless, under the department's unique interpretation of Penal Code 265.01, almost every pocketknife on the market today can be considered a gravity knife. It's as if authorities in New York City were using an antiquated law against flintlock muskets to prosecute BB-gun owners.
And the prohibition is as strict as it is all-encompassing. A knife that can be shoehorned into that definition is not only illegal to carry, it's illegal to possess at all, even within one's home. The only narrow exceptions apply to those "actively engaged" in hunting and fishing, and are essentially meaningless in New York City.